Nanomaterials are materials with particles having a diameter from 1 to 100 nanometers. The use of such nanomaterials in rubber is known from U.S. Pat. No. 4,644,988 describing a tire tread compound containing a styrene-butadiene copolymer rubber reinforced with carbon black with a particle size smaller than 20 nanometers. U.S. Pat. Nos. 6,121,346 and 6,225,397 disclose the use of silica fillers with primary particles having a particle size in the range of from 5 to 30 nanometers in a rubber also comprising zinc oxide in an amount of 2 phr to 5 phr.
A method to produce a nanoscaled zinc oxide with a mean particle diameter of from 5 nanometers to 10 nanometers starting from commercially available, comparatively cheap educts is described in DE 199 07 704 A1. These zinc oxide particles can be redispersed in water, organic solvents or mixtures with organic solvents or surface modifying substances in order to get a solution with a large extent of primary particles.
The increasing concern regarding the potential environmental and health effects of the release of zinc oxide (ZnO), which is also often accompanied by a release of cadmium, makes it desirable to reduce the ZnO content in rubber compositions, especially in rubber compositions used in the production of tires, but also to retain the positive effects of ZnO in the curing/vulcanization process.